Tipping-off operation and product



Feb. 7, 1950 R. o. MORSE ETAL 2,496,303

TIPPING-OFF OPERATION AND PRODUCT Filed July 15, 1944 INVENTORS K0. M0255 I NUf/HLL ATTORNEY Patented Feb. 7, 1950 UNITED STATES PATENT OFFICE 2,496,303 TIPPING-OFF OPERATION AND PRODUCT Rupert 0. Morse and James W. Nuttail, Hamilton, Ontario, Canada, assignors to Westinghouse 'Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 15, 1944, Serial No. 545,150

12 Claims. 1

This invention relates to tipping-off operations on evacuated envelopes and more particularly to such in which a lead extends through the exhaust tube of the envelope.

The principal object of our invention, generally considered, is to facilitate the tipping-01f operations on electrical devices in which a lead passes out of the exhaust tube.

Another object of our invention is to facilitate tipping-off operations by coating the end portion of the lead, which passes out of the exhaust tube, with graphite to the point where the tip is to be trimmed after tipping-off, whereby removal of the glass from the end portion of the lead, as for connection with a circuit, is facilitated.

A further object of our invention is to make possible a short tip on electrical devices, and especially those which are small so that the tipping-off of the exhaust tubes thereof has to be somewhat remote from the envelope in order to avoid undue heating of the latter, as by coating th end portion of the lead which passes through the exhaust tube with graphite, or other material which prevents sticking of glass thereto, so that said exhaust tube may be sealed over said lead wire to a point even beyond the end thereof, and the tip later trimmed almost to the junction between the coated and uncoated portions of the wire, with the coating facilitating removal of the trimmed off glass from said wire.

A still further object of our invention is to provide electrical devices, and particularly those small in size, in which a lead projects through the exhaust tip, the latter is relatively short, and the projecting lead portion free from glass.

Other objects and advantages of the invention,

, relating to the particular arrangement and construction of the various parts, will become apparent as the description proceeds. Referring to the scale drawing- Figure 1 is an elevational view, with parts in axial section, of a device embodying our invention, in the process of being exhausted and tipped off.

Figure 2 is an enlarged elevational view of the lower end of the lower lead of said device, also illustrating a dish of a'suspension used in applying a non-sticking coating thereto.

Figure 3 is a view corresponding to Figure 1, but illustrating'the device after it has been tipped oil.

Figure 4 is an elevational view illustrating the device of Figure 3 and a. cutting wheel in the act of removing the excess portion of the tip.

Figure 5 is a view of the same device and a rotating wire brush, in the act of removing the graphite adhering to the end portion of the wire,

Figure 6 is a view of the device of Figure 5, after the projecting end portion of the lower lead has been cleaned of graphite.

Figure 7 is an enlarged axial sectional view of the lower end portion of the exhaust tip and lead projecting therebelow.

In the manufacture of vacuum devices such as lamps, radio tubes, and other electrical devices having vitreous envelopes provided with exhaust tubes which are sealed or tipped oil. after the envelope has been evacuated, it is sometimes desirable to seal the glass of an exhaust tube around a portion of a conducting wire or lead, but to leave another portion closely adjacent to the sealed portion free of adhering glass, so that it can be used for electrical connections.

A special case of this is in the small electrical discharge device commonly known as an acorn tube. Here the exhaust tube, through which the device is evacuated, envelopes one of the leadin wires. When the operation of tipping-off is performed, the glass of the exhaust tube seals around the lead-in wire and, because of the small size of the device and the desirability of having the tip an appreciable distance from the envelope to avoid undue heating of the enclosed elements during sealing, said tip is apt to entirely enclose the extreme end portion of the wire. It then becomes necessary to cut the glass seal at the correct physical dimension in order to leave a portion of the lead-in wire available for contact with an external circuit. Heretofore this operation has consisted in nicking the glass around a complete circumference and then squeezing the part to be removed with pliers. This is an operation which must be performed with great care and skill, if only the intended glass is to be removed without disturbing the necessary vacuum-tight seal between the lead-in wire and the glass which is to remain.

Graphite has long been known as a substance 1 very useful in working glass because it is not dissolved in the glass and does not readily adhere thereto except as a thin surface layer. We have found that by applying a film of graphite, as in the form of the well-known colloidal suspension known as Aquadag, we have been able to remove the glass from part of the lead-in wire thus trimmed much more readily, with the use of much less skill than by any method known to us heretofore, and with much less loss by breakage.

Referring to the drawing in detail, Figure 1 represents an acorn tube H, in the tipping-off position on an exhausting machine l2, and with its exhaust tube i3 received in an exhaust rubber l4. In making this and other similar tubes, it is highly desirable in order to maintain the elec- 3 trical characteristics of the device to separate as much as possible the lead-in wires i5 and I8 from each other and from other lead-in wires |'I. Lead-in wire IE to the anode I8 of the device is sealed to the vitreous or glass bulb or envelope 2| by ordinary methods before the device is evacuated, as the tubulation on the upper end of the bulb is sufficiently short to prevent glass adhering to more than a short length of said lead-in wire, thereby allowing a necessary length of bare wire to project from the envelope as illustrated.

However, the lower lead-in wire IS in the present instance extends down into exhaust tube l3, so that in normal tipping-off operations the exhaust fires l9 tend to, not only seal the exhaust tube around the lead, but completely melt it over even the extreme lower end of said lead, thereby ordinarily making it impossible to connect with said lead after tipping-off without removing some of the glass of the tip. This is particularly true in small tubes where it is not desired that the fires i9 get too close to the envelope 2|, so as to avoid undue heating of the enclosed elements or leads I I projecting from the lower portion thereof, the latter of which may serve to support the tube during the tipping-ofi operation.

Accordingly, we coat the lower, free, or exterior end portion of the lead IS with a material 22 which prevents the vitreous material or glass which is to enclose the wire from sticking thereto after being fused in contact therewith and, at the same time, is refractory or not readily removed by heating. This material is desirably graphite and may be applied in the form of a suspension such as that prepared by diluting Aquadag" "Aquadag consists of approximately 20% total solids, which are principally defiocculated graphite, and 80% water, with a small amount of tannin added to hold the graphite in suspension. The diluting material which we have employed is methanol, although ethyl alcohol or some other thinner or mixture may be substituted if desired. The concentration which we have employed ranges from 1 gram of Aquadag" diluted by 1 milliliter of methanol, to 1 gram of "Aquadag diluted by 6 milliliters of methanol, but it is probable that other concentrations beyond this range could be successfully employed. Such other possibilities however have not been investigated because of the highly satisfactory manner in which the invention has been practiced.

A mixture containing a high proportion of Aquadag was found to promote facility in breaking the glass away from the lead, while a mixture of lower concentration was found to be more readily applied in controlled amounts. A preferred mixture containing 1 gram of "Aquadag diluted by 3 milliliters of methanol combines the desirable features of both of the above mentioned extremes to a high degree.

The method which we adopted to apply the coating to the lead was that of dipping, as illustrated in Figure 2, so that the lower end of the lead it engages the bottom of the vessel or dish 23, indicated in dotted lines and containing the Auuadag suspension 24, the level of the upper surface of the suspension determining the position of the junction between the coated and bare portions of the lead. However, we do not wish to limit ourselves to this method of coating.

The envelope 2| of the present embodiment is made from two parts, that is, a lower cup part or that below the leads l1 and carrying the relatively long exhaust tube It, and an upper inverted cup part 28 carrying a short upper tubulation through which the lead I! may extend. After the interior metal elements of the tube H, such as the anode l8 and enclosed cathode with its grid or grids (not shown) are assembled and electrically connected and structurally secured and aligned, the lead l6, depending therefrom, is coated in any desired manner such, for example, as illustrated in Fig. 2.

The assembled parts are then placed in the lower envelope portion, so that said graphitecoated lead extends into the exhaust tube it, as illustrated in Fig. 1. The leads II project radially outward, with their outer ends desirably connected to a supporting ring (not shown) and resting on the upper edge of the lower envelope portion, which may have an outstanding upper or colloidally dispersed graphite.

peripheral lip. I

The upper envelope portion 20, which may have a corresponding lower peripheral lip portion, is then placed over to enclose the anode ll, so that the lead l5 therefrom projects through its short tubulation, and its lip portion, if occurring, overlies the lip portion, if occurring, of the lower section of the envelope, with the leads held between the adjacent edges or lip portions. The matching edges of the envelope portions are then sealed around their circumferences to produce the main seal 40 of the tube, with the leads embedded therein, and the upper lead I! is sealed through the short tubulation of the upper part of the envelope. The envelope 2|, is thus hermetically sealed at all points, except the opening through the exhaust tube l3 containing the graphite-coated lead l8. The device is then suiiiciently exhausted, and the fires I! used to seal the exhaust tube I; about the lower end portion of the lead It.

Ordinarily the glass entirely encloses the lead after tipping-oil, as shown in Figure 3, the length of the seal being such that a vacuum-tight connection is produced between the bare portion of the lead II and the glass of the exhaust tube l2, even with the fires maintained a substantial distance below the envelope 2|, and the tip extending to the extreme lower end of the lead l6.

Figure 4 shows the next operation which is the employment of a glass cutting wheel 25 of pref erably .02 inch thickness against which the periphery of the exhaust tube, now sealed about the lead-in i8 wire, is held and a circumferential cut made at a point near the inward extremity of the graphite coating 22, but slightly outward of the iunction between the coated and bare portions of the lead ll. The cutting wheel 25 is shown attached rigidly, as by means of bushings 26 and 21 and nut 22, to its shaft 29 which is rotated as indicated by the arrow 30 by means of a motor (not shown) at about 1750 R. P. M. with a cutting wheel six inches in diameter.

After this circumferential cut is made, the extreme end of the hermetically sealed exhaust tube II is broken 03 and crushed, as by means of a pair of pliers. Since the graphite has little cohesion within itself, the glass broken of! drops away from the lead wire at its graphite-coated extremity. Part of the graphite adheres to the leadin wire and part to the broken fragments of glass beyond the cut made by the wheel 25.

Figure 5 shows the operation of removing the graphite coating from the portion of the lead-in wire, projecting beyond the seal between the exhaust tube It and said wire inwardly of the cut, by means of a wire brush 2| secured to a shaft 32,

indicated as rotating by the arrow 80, between bushings 33 and 34 by nut 35.

Figure 6 shows the completed lamp with the projecting or bare portion of the lead-in wire it cleaned and ready for connection with a circuit. An enlarged detail of this lead It and its seal with the exhaust tube It is illustrated in Figure '7.

In further experimenting in the use of graphite, we find that by applying it to the exposed part of the lead-in wire l5, oxidation of this part is greatly reduced, and the graphite itself, together with the reduced amount of oxide, can be removed much more readily than the heavy oxide previously formed when there was no coating with graphite. This may further be extended, for example in the case of devices which have three parallel lead-in wires remote from that which is sealed through the exhaust tube, which may be thus treated to advantage.

Although we have shown this improvement using grapite with a small tube, we do not limit ourselves thereto as similar use may be made in connection with the manufacture of larger tubes, such asthose for transmitting purposes where intense heat is brought to bear at points near conductors which are to be used for electrical contacts.

Although a preferred embodiment of our invention hasbeen disclosed it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim:

1. The method of sealing an evacuated device, in which a lead therefrom extends into a vitreous exhaust tube thereof, comprising coating the free end portion of said lead with refractory material which prevents vitreous material from sticking thereto after being fused in contact therewith, leaving the adjacent portion uncoated, heating said exhaust tube to form a vacuum-tight seal with the uncoated portion of said lead adjacent the coated portion, in which the material of said exhaust tube is fused to cover at least a part of the coating on said lead, and cutting the vitreous material of said seal at a point very near the junction between, the coated and uncoated portions, but slightly toward the free end of said lead, so that it is thereafter easy to remove the portion over the coated lead.

2. The method of sealing an evacuated device, I

in which a lead therefrom extends into a vitreous exhaust tube thereof, comprising coating the free end portion of said lead with graphite, leaving an adjacent portion uncoated, heating said exhaust tube to form a vacuum-tight seal with the uncoated portion of said lead adjacent the coated portion, in which the material of said exhaust tube is fused to cover at least a part of the coating on said lead, and cutting the vitreous material of said seal at a point very near the junction between, the coated and uncoated portions, but slightly toward the free end of said lead, so that it is thereafter easy to remove the portion over v the coated lead.

3. An evacuated envelope, an exhaust tube ex tending therefrom, a lead disposed in said exhaust tube, the outer end portion of said lead being coated with graphite, and said exhaust tube sealed thereto and covering said graphite-coated portion and the adjacent part of the bare portion of said lead.

4. A seal between a vitreous exhaust tube and an enclosed wire to form a lead, in which the free iii sticking thereto after being fused in contact therewith, and the exhaust tube completely sealed over said refractory-coated portion and a part of the bare wire adjacent thereto.

5. A seal between a vitreous exhaust tube and an enclosed wire to form a lead, in which the outer end portion of said wire is coated with graphite and the exhaust tube completely sealed over said graphite-coated portion and a part of the bare wire adjacent thereto.

6. The method of manufacturing an electrical device comprising coating only a short length at thefree end of the metal lead, extending from an interior metal element of said device, with refractory material which prevents vitreous ma terial from sticking thereto after being fused in contact therewith, placing the interior metal elements of said device, including that from which the lead extends, so that they are supported and the partially-coated lead extends into a vitreous exhaust tube of the lower portion of a vitreous envelope for said device, placing the upper portion of said vitreous envelope in matching relationship over said metal elements, hermetically sealing the envelope, including the matching edges of the upper and lower portions around their circumferences, except for the opening through said exhaust tube, evacuating the envelope through said exhaust .tube, heating said exhaust tube to form a vacuum-tight seal with the bare portion of said lead adjacent the coated portion, in which the material of said exhaust tube is fused to cover at least a part of the coating on said lead, and cutting the vitreous material of said seal at a point very near the junction between, the coated and bare portions, but slightly toward the free end of said lead, so that it is thereafter easy to remove the portions over the coated lead.

7. The method of manufacturing an electrical device comprising coating only a short length at the free end of a metal lead, extending from an interior metal element of said device, with refractory material which prevents vitreous material from sticking thereto after being fused in contact therewith, placing the interior metal elements of said device, including that from which the lead extends, so that they are supported and the partially-coated lead extends into a vitreous exhaust tube of the lower portion of a vitreous envelope for said device, placing the upper portion of said vitreous envelope in matching relationship over said metal elements, hermetically sealing the envelope, including the matching edges of the upper and lower portions around their circumferences, except for the opening through said exhaust tube, evacuating the envelope through said exhaust tube, heating said exhaust tube to form a vacuum-tight seal with the bare portion of said lead adjacent the coated portion, in which the material of said exhaust tube is fused to cover at least a part of the coating on said lead, cutting the vitreous material of said seal at a point very near the junction between, the coated and bare portions, but slightly toward the free end of said lead, and crushing the vitreous material beyond the cut and along the coated wire portion to cause its removal therefrom.

8. The method of manufacturing an electrical device comprising coating only the free-end portion of a metal lead, extending from interior metal elements thereof, with refractory material for preventing vitreous material from sticking thereto, after being fused in contact therewith, placing said interior metal elements so that they are supported by leads extending laterally thereasoasos erally extending leads in the formed seal, sealing the upper lead through said top tubulation in the upper part of the envelope, evacuating the envelope through said exhaust tube, heating said exhaust tube to form a vacuum-tight seal, with the bare portion of said partially-coated lead, in

which the material of said exhaust tube is melted over at least a part of the coating on said lead, and cutting off the vitreous material of said seal at a point slightly outward of, but very near, the

junction between the coated and bare portions of said lead, so that the coating makes it easy to remove the cut-off portions.

9. The method of manufacturing an electrical device comprising coating only a short length at the free end of a metal lead extending from an 5 interior metal element of said device with refractory material which prevents glass from sticking thereto after being fused incontact therewith, placing the interior metal elements of said device, including that from which the lead extends,

so that they are supported and the end-coated lead extends into a glass exhaust tube of the lower portion of a glass envelope for said device, placing the upper portion of said glass envelope in matching relationship over said metal elements, hermetically sealing the envelope including the matching edges of the upper and lower portions around their circumferences, except for the opening through said exhaust tube, evacuating the envelope through said exhaust tube, heating said exhaust tube to form a vacuum-tight seal with the bare portion of said lead adjacent the coated portion, in which the material of said exhaust tube is fused to cover at least a part of the coating on said lead, and cutting the glass of said seal at a point very near the junction be.- tween, the coated and bare portions, but slightly toward the free end of said lead.

10. The method of manufacturing an electrical device comprising coating with graphite only a short length at the free end of a metal lead extending from an interior metal element of said device, placing the interior metal elements of said device, including that from which the lead extends, so that they are supported and the partially-coated lead extends into a vitreous exhaust tube of the lower portion of a vitreous envelope for said device, placing the upper portion of said vitreous envelope in matching relationship over said metal elements, hermetically sealing the enw velope, including the matching edges of the upper and lower portions around their circumferences, except for the opening through said exhaust tube, evacuating the envelope through said exhaust tube, heating said exhaust tube to form a vace5 uum-tight seal with the bare portion of said lead adjacent the coated portion, in which the ma terial of said exhaust tube is fused to cover at least a part of the graphite coating on said lead,

and cutting the vitreous material of said seal at 2,174,374

device comprising coating with graphite only a 7g short length at the free end of a metal lead extending from an interior metal element of said device, to prevent glass from sticking thereto after being fused in contact therewith, placing the interior metal elements of said device, including that from which the lead extends, so that they are supported and the partially coated lead extends into a glass exhaust tube of the lower portion of a glass envelope for said device, placing the upper portion of said glass envelope in matching relationship over said metal elements, hermetically sealing the envelope including the matching edges of the upper and lower portions around their circumferences, except for the opening through said exhaust tube, evacuating the envelope through said exhaust tube, heating said exhaust tube about said lead to form a vacuumtight seal with the bare portion thereof adjacent said coated portion, in which the glass of said tube is fused to cover at least a part of the coating on said lead, and cutting the glass of said seal at a point very near the Junction between the coated and bare portions, but slightly toward the free end of said lead.

12. The method of manufacturing an electrical device comprising coating with graphite only the free-end portion of a metal lead, extending from interior metal elements thereof, placing said interior metal elements so that they are supported by leads extending laterally therefrom, resting on the upper edge, and the coated lead extends into an exhaust tube, of the lower portion of a glass envelope for said device, placing the upper portion of said envelope over said metal elements, so that an upper lead therefrom projects through a tubulation at the top of said upper portion, sealing the matching edges of the upper and lower envelope portions around their circumferences, while embedding the laterally extending leads in the formed'seal, sealing the top tubulation about said upper lead, evacuating the envelope through said exhaust tube, heating said exhaust tube to form a vacuum-tight seal with the bare portion of said partially-coated lead, in which the glass of said tube is melted over at least a part of the graphite on said lead, making a circumferential cut around said exhaust tube at a point near the junction between the coated and bare portions of said lead, but slightly toward the free end of the latter, and crushing the glass beyond said out and along the coated lead portion to cause it to drop therefrom.

RUPERT O. MORSE. JAMES W. NUI'IALL.

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